Chloride and Its Clinical Implications in Today's Clinical Practice: Not an Orphan Electrolyte

Home , Delta ratio, Hyperchloremia, Hypochloremia, Pathophysiology, Serum chloride

rology & h T ep h e Goel, J Nephrol Ther 2015, 5:6 N r f a o p l e a

u DOI: 10.4172/2161-0959.1000223

r i

o J

ISSN: 2161-0959 Journal of Nephrology & Therapeutics

Review Article Open Access Chloride and its Clinical Implications in Today’s Clinical Practice: Not an Orphan Electrolyte Narender Goel* Middletown Medical PC, 111, Maltese Drive, Middletown NY, USA; Consultant at Orange Regional Medical Center, NY, USA; Adjunct Clinical Assistant Professor (Internal Medicine and Nephrology) at Touro College of Osteopathic Medicine, New York, USA

Abstract Though chloride is the predominant extracellular anion, it is mostly seen just as an anion accompanying sodium and hardly receives attention in textbooks. But independent evaluation of serum chloride may unearth several clinical and acid-base disorders. It is used in formulas to estimate serum anion gap, urine anion gap, and strong ion difference (Stewart method). Several critical functions of a cell such as maintenance of cell volume, neutralization of H+ in lysosomal vesicles, epithelial fluid transport, change in cell membrane potential and ligand-gated transmission in the post-synaptic membrane utilize chloride channels. In addition, chloride forms an integral part of anion exchanger proteins coded by SLC26A gene family. Chloride is an essential component of intravenous fluids used in day-to-day clinical practice. The role and contribution of chloride rich fluids and resulting acidosis in causing inferior outcomes in sepsis, renal vasoconstriction, and acute kidney injury has been debated. Numerous genetic diseases are known to be related with chloride channels and proteins abnormalities. In the following review, I would like to bring much needed attention towards importance of chloride in human physiology. The following hypothetical clinical case will be just a spark for fiery chloride.

Keywords: Hyperchloremia; Hypochloremia; Anion exchanger; receives attention in textbooks. But, independent evaluation of serum Chloride channel chloride may unearth several clinical and acid-base disorders. Chloride significantly contributes to plasma tonicity and is used in formulas to Introduction estimate serum anion gap, urine anion gap, and strong ion difference (Stewart method) [3] which is less popular for use in clinical practice Case 1: An 18 years old male was brought to ER in an obtunded state. due to its complex interpretations. He had an alcoholic smell on his breath and was hemodynamically stable with a blood pressure (BP) of 110/60 mmHg. His physical examination Urine Anion Gap = urine [Na+ + K+] – Cl– ------(eq.4) was unremarkable except for him being drowsy. Preliminary laboratory Strong ion difference = (Na+ + K+ + Mg++ + Ca++) – (Cl– + lactate + results were as follows; Serum sodium 139 meq/L, potassium 5 meq/L, other strong anions) ------(eq.5) bicarbonate 22 meq/L, chloride 87 meq/L and glucose of 90 mg/ dL. Blood alcohol level was undetectable and urine microscopy was Na+, K+, Cl–, HCO3– in meq/L significant for oxalate crystals. A diagnosis of poisoning with anti- The role of chloride in urine anion gap measurements is unique freeze (ethylene glycol) was made. + and indirect as chloride here is serving as a surrogate marker of NH4 In this patient most of these laboratory information seems excretion in urine. A positive urine anion gap in the presence of normal however serious acid-base disorder can be easily overlooked metabolic acidosis is often abnormal and points towards low urinary + if attention is not paid towards the remarkably low chloride value NH4 excretion, thus impaired urinary acid excretion. which is suggesting here a complex acid base disorder with high anion gap metabolic acidosis (serum anion gap of 30) and superimposed Chloride Physiology metabolic alkalosis (delta gap of 18 and delta ratio of 10). The high During early experiments, hyperchloremia was found to be anion gap pointed towards unmeasured anions which were later found associated with renal vasoconstriction and fall in glomerular filtration to be oxalic acid, the metabolite of ethylene glycol. rate that was independent of renal sympathetic nervous activity [4]. Serum Anion Gap = serum Na+ – [Cl– + HCO3–] ------Now it is known that functions and physiochemical actions of chloride -- (eq.1) are mediated via chloride channels (ClC), which participates in several critical functions of a cell such as maintenance of cell volume (volume Delta gap= Measured anion gap – Normal anion gap – sensitive ClC), neutralization of H+ in lysosomal vesicles (ClC3, ClC5, Normal [HCO3–] – Measured [HCO3–] ------(eq.2) ClC7), epithelial fluid transport (CFTR, ClC-Ka, ClC-Kb), change in cell membrane potential (ClC1, ClC2, calcium-ClC) and ligand gated

------(eq.3) *Corresponding author: Narender Goel, Middletown Medical PC, 111, Maltese Na+, Cl– and HCO3– in meq/L Drive, Middletown NY-10940, USA, Tel: +1 845-342-4774; Fax: +1 845-343-8116; E-mail: [email protected] Chloride is the predominant extracellular anion with normal Received: October 01, 2015; Accepted: October 29, 2015; Published: November 05, 2015 concentration ranging from 94-111 meq/L [1]. It is commonly ingested as table salt (sodium chloride). In early experiments, it was determined Citation: Goel N (2015) Chloride and its Clinical Implications in Today’s Clinical Practice: Not an Orphan Electrolyte. J Nephrol Ther 5: 223. doi:10.4172/2161- that chloride’s total body concentration was 30 meq/Kg body weight 0959.1000223 and intracellular concentration was 24.8 meq/L of cell water which Copyright: © 2015 Goel N. This is an open-access article distributed under the was 29.7% (range 19.8-40.4%) of total body chloride [2]. Chloride terms of the Creative Commons Attribution License, which permits unrestricted is mostly seen just as an anion accompanying sodium and hardly use, distribution, and reproduction in any medium, provided the original author and source are credited.

J Nephrol Ther Volume 5 • Issue 6 • 1000223 ISSN: 2231-0959 JNT, an open access journal Citation: Goel N (2015) Chloride and its Clinical Implications in Today’s Clinical Practice: Not an Orphan Electrolyte. J Nephrol Ther 5: 223. doi:10.4172/2161-0959.1000223

Page 2 of 4 transmission in the post-synaptic membrane (GABA and glycine anion exchanger-1) plays crucial role in red blood cells in maintaining channels) [5-7]. In the mouse models, function of aquaporin-6 is also electro-neutrality [11]. Another unique chloride channel is cystic shown to involve chloride transport [7]. Macula densa cells perform fibrosis transmembrane conductance regulator (CFTR) that is a located their crucial function of tubuloglomerular feedback by sensing chloride in apical membrane of epithelia and involved in transepithelial salt concentration in tubular fluid [8]. Chloride also forms an integral transport, fluid flow, and ion concentration [12]. Parchorin is a recently part of SLC26A anion exchanger protein. Chloride is also an essential discovered intracellular chloride channel in water secreting cells such component of intravenous fluids used in day-to-day clinical practice as salivary glands, lachrymal glands, pancreas, cochlea and kidneys and it concentration in different replacement fluids (mmol/L) is as whereby it plays a critical role in water secretion by regulation of follows [1]: chloride transport. Prestin is another SLC25A5 gene encoded chloride/ bicarbonate anion exchanger protein and present on outer hair cells of 4% Albumin= 128; Normal saline (0.9%) = 154, Half normal saline cochlea [13]. (0.45%) = 77, Ringers lactate= 111, PlasmaLyte= 98, Hydroxyethyl starch= range 110-154 Causes of chloride disorders Finally, the role and contribution of chloride rich fluids and Hypochloremia: Low serum chloride is often associated with resulting acidosis in causing inferior outcomes in sepsis [3], renal metabolic alkalosis that could be due to volume loss from gastric vasoconstriction [3] and acute kidney injury [9] has been debated [3]. content as gastric fluid is rich in chloride (Cl–) along with proton (H+) both of which together forms hydrochloric acid [3] or from kidneys Handling of chloride by the kidneys such as due to diuretics or salt wasting nephropathies (Bartter and Approximately 21000 meq of chloride is filtered everyday of which Gitelman Syndrome) [14]. >99% is absorbed (55% in proximal tubule, 25-35% in thick ascending In these cases, chloride depletion also plays a crucial role in loop (TAL) of Henle and rest in distal tubule) and only 100-250 meq is maintaining metabolic alkalosis. Decreased delivery of chloride to the excreted every day [10]. Once in proximal tubular lumen, chloride is macula densa stimulates renin release which activates angiotensin and reabsorbed actively via anion exchanger [SLC26A6] (chloride-formate, aldosterone and thereby promotes proton excretion in the distal tubule. chloride-hydroxyl, chloride-oxalate exchanger) on luminal side and + - The lower chloride concentration in the tubular lumen also impairs leave the cells via K Cl co-transporter and chloride selective channels – – activity of luminal Cl -HCO3 exchanger in type B intercalated cell and [10]. Chloride is also reabsorbed passively across tight junctions in – + – leads to reduced excretion of HCO3 , exacerbating metabolic alkalosis proximal tubule [10]. In the proximal tubule, ClC5 (H /Cl antiporter) further. helps to secretes H+ into endosomes and maintain low pH that is necessary for protein degradation [5-7]. Hypochloremia and metabolic alkalosis may be associated with volume overload conditions such as edema, congestive heart failure, In TAL, chloride is reabsorbed via luminal Na-K-2Cl cotransporter nephrotic syndrome and mineralocorticoid excess [14]. Finally, and leaves the cell via ClC-Ka channel co-localized with Barttin protein. hypochloremia also often accompanies hyponatremia [3]. Additionally, Furosemide that is a loop diuretic, works on TAL via competing for a case series of 3 patients has been reported whereby hypochloremia binding to chloride site on the Na-K-2Cl cotransporter. Reabsorption and hyponatremia was the initial presentation of cystic fibrosis [15]. of sodium chloride in TAL is essential for generation of medullary osmotic gradient, a pre-requisite for excreting concentrated urine. As seen in case 1, hypochloremia in the presence of seemingly normal other electrolytes points towards complex acid base disorders Once tubular fluid reaches macula densa, its activity is modulated such as high anion gap metabolic acidosis and superimposed metabolic by chloride concentration such that low chloride concentration alkalosis. activates macula densa cells and thereby stimulates renin release. In distal convoluted tubule, chloride is actively reabsorbed via luminal Hyperchloremia: Serum chloride level is usually elevated in Na-Cl cotransporter and leaves the cell via basolateral chloride channel inorganic metabolic acidosis and signifies normal-anion gap metabolic [11]. Chloride may be absorbed by paracellular route as well. WNKs acidosis (NAGMA). Differential of NAGMA often includes an inability (with no lysine [K]) are the unique serine/threonine kinases and of the kidneys to excrete an acid load into the urine (renal tubular recently known to regulate activity of Na-Cl cotransporter in distal acidosis) or gastrointestinal loss of bicarbonate due to diarrhea, tubule. Thiazide diuretics which work in distal tubule acts by blocking ureteroenteric fistula or pancreato-duodenal fistula, which can be easily Na-Cl cotransporter activity. differentiated measuring urine anion gap (eq. 4) which is positive in renal tubular acidosis due to impaired NH4+ excretion. Other causes In the collecting tubule, principal cell absorbs sodium via of NAGMA may include hyper-alimentation, intravenous infusion of epithelial sodium channel (ENaC) and creates electronegative lumen chloride rich fluid such as 0.9% normal saline, medications such as that stimulates paracellular chloride reabsorption, which if increased carbonic anhydrase inhibitors, ENaC blockers (triamterene, amiloride) significantly, may impair potassium and proton secretion due to loss or poisoning with toluene, isopropyl alcohol, and salicylates. of electrochemical gradient. Type A intercalated cell has basolateral – – – Cl -HCO3 exchanger (SLC4A1) which extrudes HCO3 outside the cell Hypernatremia due to dehydration or diabetes insipidus is also in exchange for in-coming chloride ion, whereas type B intercalated often accompanied with elevated chloride level [3]. Spuriously elevated – – cell has Cl -HCO3 exchanger (SLC26A4) [3,6] also known as Pendrin, chloride level may be seen in toxicity with salicylic acid [16] and – located at luminal side which secretes HCO3 into the tubular lumen in bromide [17] to the extent that the anion gap may be erroneously exchange for chloride [11]. These are the crucial transporters involved reported to have a greatly negative value. in distal tubular proton excretion. Genetic diseases associated with chloride channels and Beside kidneys, ClC-Ka and CLC-Kb in the stria vascularis in the exchangers: Numerous genetic diseases as mentioned briefly below are inner ear are involved in chloride recycling and their mutation leads known to be related with chloride channels and proteins abnormalities. – – to congenital deafness [5,6]. Also, Cl -HCO3 exchanger (band-3 or

Page 3 of 4

Bartter Syndrome: It is a salt wasting nephropathy and an autosomal a necessary step for synthesis of thyroid hormones. Pendrin is also recessive disorder. It is characterized by hypokalemia, metabolic expressed in in the inner ear and plays crucial role in homeostasis of alkalosis, hypochloremia, polyuria and hypercalciuria. Bartter syndrome endolymph, the fluid bathing neurosensory hair cells [22]. type I that commonly presents during early life, is due to mutations in Cystic Fibrosis: It is an autosomal recessive disorder due to mutation SLC12A1 gene that leads to defective Na-K-2Cl cotransporter. Bartter in CFTR [5,6,12], a unique chloride channel and clinically characterized syndrome type III has mutation in CLCNKB gene and ClC-Kb channel by growth impairment, infertility, pancreatic insufficiency, recurrent [6,7]. Bartter syndrome Type IV has mutation in Barttin which is a lung infections, elevated concentration of chloride in sweat and β-subunit of ClC-Ka and ClC-Kb channels which is also associated malabsorption. with sensorineural deafness (Bartter with sensorineural deafness). Bartter syndrome type II is caused by mutation in luminal potassium Since chloride forms an integral part of anion exchanger proteins channel, ROMK (renal outer medullary potassium). It leads to impaired coded by SLC26 gene, various other genetic diseases in association recycling of cellular potassium into the tubular lumen, thus inhibiting with abnormal chloride exchangers have been identified. These include luminal Na-K-2Cl cotransporter [18]. diastrophic dysplasia (mutations in the SLC26A2 gene), congenital chloride diarrhea (mutations in the SLC26A3 gene) and deafness Gitelman Syndrome: It is also a salt wasting nephropathy, but milder (mutations in the SLC26A5 (prestin) gene) [23]. form as compared to Bartter syndrome and is an autosomal recessive disorder caused by mutation in SLC12A3 gene and distal tubular Na- Clinical Approach Cl cotransporter. It is also characterized by hypokalemia, metabolic Symptoms related to derangement in chloride level usually depend alkalosis, hypochloremia, polyuria, but hypocalciuria and tends to upon underlying cause and hence treatment also widely varies. present later in life [18]. Hypochloremia: The initial diagnostic step in patients with Gordon Syndrome: Also known as familial hyperkalemic hypochloremia and metabolic alkalosis is to assess urinary chloride hypertension or pseudohypoaldosteronism type 2, it has activating which if <20 meq/L suggest hypovolemia and also known as chloride- mutation in WNK 1 and inactivating mutation in WKN4 (autosomal sensitive metabolic alkalosis. Patients promptly respond to volume dominant) protein that leads to over activity of distal tubular luminal replacement with normal saline and correction of the underlying Na-Cl cotransporter activity. It is clinically characterized by severe etiology such as cessation of diuretics, nasogastric suction, or vomiting. form of low renin and low aldosterone hypertension, hyperkalemia, and hyperchloremic metabolic acidosis [19]. If urine chloride is >40 meq/L (chloride resistant metabolic alkalosis) it suggests either salt wasting nephropathy such as Bartter Dent disease: It is an X-linked recessive disorder due to inactivating or Gitelman syndrome which can be distinguished by urinary calcium mutation in ClC5 channel (H+Cl– antiporter) [5-7] which causes excretion or volume overload states such as congestive heart failure, impaired protein degradation in the proximal tubule and leads to hyperaldosteronism or apparent mineralocorticoid excess which can proximal tubular dysfunction, hypercalciuria, proteinuria, rickets or be differentiated with clinical history, physical exam, echocardiogram osteomalacia, nephrocalcinosis and chronic kidney disease [5]. and measurement of serum aldosterone level along with plasma renin activity or concentration. Osteopetrosis: Also known as Marble Bone Disease, it has mutation in CLC7 in osteoclasts endosomes and leads to disease due to inability In a patient with hypochloremia with normonatremia and normal or to maintain low pH intracellularly [5]. It can have heterogeneous low serum bicarbonate, serum anion gap (eq. 1) and delta gap (eq. 2) or presentation and involve growth disorder, bone, hematopoietic and delta ratio (eq. 3) should be routinely measured which will uncover the neurological abnormalities [20]. mixed acid base disorders as seen in case 1. If poisoning with alcohols is suspected, serum osmolar gap (eq. 6,7) also should be calculated. Polycystic kidney disease: PCKD is an autosomal dominant disease However, in patients with hypochloremia and hyponatremia, the that is caused by mutation in PKD1 and PKD 2 gene and may mediate primary focus should be shifted towards hyponatremia management. via c-AMP dependent chloride secretion in to cysts [7]. It is clinically Serum Osmolar Gap = Calculated Serum Osmolarity – measured characterized by development of multiple cysts in each kidney and serum osmolarity ------(eq.6) chronic kidney disease and other extra-renal manifestations such as arterial aneurysms and extra-renal cysts. Calculated Serum Osmolarity (mosm/kg) = 2 [Na+] + BUN/2.8 + Glucose/18 + Ethanol/4.6 ------(eq. 7) Renal tubular acidosis (distal): It is predominantly an autosomal dominant mutation in AE1 gene and basolateral anion exchanger Cl–- Na+ (meq/L), BUN, glucose and ethanol (mg/dL) HCO – in the distal tubule. Some autosomal recessive forms are also 3 Hyperchloremia: It is characterized by high concentration of serum described and rare association with hemolytic anemia is also noted. It chloride. In all patients, serum anion gap (eq. 1) and delta gap (eq. is clinically characterized by impaired urinary acidification, non-anion 2) or delta ratio (eq. 3) should be routinely calculated. If poisoning gap hyperchloremic metabolic acidosis, hypokalemia, hypercalciuria, with toluene is suspected, urine osmolar gap (eq. 8,9) also should nephrocalcinosis, nephrolithiasis, bone demineralization, and growth be calculated. In the patients with greatly elevated chloride level and retardation [21]. negative serum anion gap, toxicity with salicylate or bromide should be Pendred syndrome: It is an autosomal recessive involving mutation suspected and their level should be checked [16,17] in Pendrin (SLC26A4/PDS gene) and clinically characterized by Urine Osmolar Gap = Calculated Urine osmolarity – measured bilateral sensorineural hearing loss and goiter. Pendrin is an anion urine osmolarity ------(eq. 8) exchanger antiporter protein and function as iodide/chloride exchanger + + in thyroid follicular cells, whereby it help in secreting iodide in colloids, Calculated Urine Osmolarity (mosm/kg) = 2 [Na +K ] + BUN/2.8 + Glucose/18 ------(eq. 9)

Page 4 of 4

Na+, K+ (meq/L), BUN & glucose (mg/dL) 8. Salomonsson M, Gonzalez E, Kornfeld M, Persson AE (1993) The cytosolic chloride concentration in macula densa and cortical thick ascending limb cells. In patients with hyperchloremia and metabolic acidosis, patients Acta Physiol Scand 147: 305-313. usually have normal-anion gap metabolic acidosis that could be either 9. Yunos NM, Bellomo R, Hegarty C, Story D, Ho L et al (2012) Association – between a chloride-liberal vs chloride-restrictive intravenous fluid administration due to gastrointestinal losses or renal loss of HCO3 or renal inability to acidify urine. This can be differentiated using urine anion gap (eq. 4) strategy and kidney injury in critically ill adults. JAMA 308: 1566-1572. and urine osmolar gap (eq. 8,9). 10. Rose BD, Post TW (2001) Introduction to renal function: Clinical physiology of acid-base and electrolyte disorders. (5th edtn), McGraw-Hill, USA.

Conclusion 11. Rose BD, Post TW (2001) Renal Physiology: Clinical physiology of acid-base Disorders of chloride may present in isolation or along with other and electrolyte disorders, (5th edtn), McGraw-Hill, USA. electrolyte abnormalities. Either way, it has great clinical significance in 12. Sheppard DN, Welsh MJ (1999) Structure and function of the CFTR chloride day-to-day practice. Complex acid base disorders and pathophysiology channel. Physiol Rev 79: S23-45. of a clinical presentation can be missed if enough attention is not 13. Izzedine H, Tankere F, Launay-Vacher V, Deray G (2004) Ear and kidney towards chloride concentration. Knowledge and research on chloride syndromes: molecular versus clinical approach. Kidney Int 65: 369-385. channels has unraveled numerous genetic diseases. Now, it’s time for 14. Galla JH (2000) Metabolic alkalosis. J Am Soc Nephrol 11: 369-375. chloride to receive much needed attention and not be left alone as an 15. Priou-Guesdon M, Malinge MC, Augusto JF, Rodien P, Subra JF, et al. (2010) orphan electrolyte. Hypochloremia and hyponatremia as the initial presentation of cystic fibrosis in three adults. Ann Endocrinol (Paris) 71: 46-50.

References 16. Jacob J, Lavonas EJ (2011) Falsely normal anion gap in severe salicylate poisoning caused by laboratory interference. Ann Emerg Med 58: 280-281. 1. Myburgh JA, Mythen MG (2013) Resuscitation fluids. N Engl J Med 369: 1243- 1251. 17. Bowers GN Jr, Onoroski M (1990) Hyperchloremia and the incidence of bromism in 1990. Clin Chem 36: 1399-1403. 2. Deane N, Ziff M, Smith HW (1952) The distribution of total body chloride in man. J Clin Invest 31: 200-203. 18. Fremont OT, Chan JC (2012) Understanding Bartter syndrome and Gitelman syndrome. World J Pediatr 8: 25-30. 3. Yunos NM, Bellomo R, Story D, Kellum J (2010) Bench-to-bedside review: Chloride in critical illness. Crit Care 14: 226. 19. Garovic VD, Hilliard AA, Turner ST (2006) Monogenic forms of low-renin hypertension. Nat Clin Pract Nephrol 2: 624-630. 4. Wilcox CS (1983) Regulation of renal blood flow by plasma chloride. J Clin Invest 71: 726-735. 20. Tolar J, Teitelbaum SL, Orchard PJ (2004) Osteopetrosis. N Engl J Med 351: 2839-2849. 5. Suzuki M, Morita T, Iwamoto T (2006) Diversity of Cl(-) channels. Cell Mol Life Sci 63: 12-24. 21. Batlle D, Haque SK (2012) Genetic causes and mechanisms of distal renal tubular acidosis. Nephrol Dial Transplant 27: 3691-3704. 6. Jentsch TJ, Maritzen T, Zdebik AA (2005) Chloride channel diseases resulting from impaired transepithelial transport or vesicular function. J Clin Invest 115: 22. Toriello HV, Smith SD (2013) Hereditary hearing loss and its syndrome. (3rd 2039-2046. edtn)Oxford University Press, USA.

7. Devuyst O, Guggino WB (2002) Chloride channels in the kidney: lessons 23. Alper SL, Sharma AK (2013) The SLC26 gene family of anion transporters and learned from knockout animals. Am J Physiol Renal Physiol 283: F1176-1191. channels. Mol Aspects Med 34: 494-515.

J Nephrol Ther Volume 5 • Issue 6 • 1000223 ISSN: 2231-0959 JNT, an open access journal